1. Field of the Invention
The present invention relates to a photosensitive heat-resistant resin composition. The present invention also relates to a method of patterning a heat-resistant insulating film made of such a resin composition. The present invention further relates to a patterned heat-resistant insulating film.
More specifically, a photosensitive heat-resistant resin composition according to the present invention contains a polyamideimide and an acrylic resin as main components. The polyamideimide is excellent in heat-resistance, electrical insulation and toughness, whereas the acrylic resin has a nature of polymerizing or hardening under light irradiation. Thus, the resin composition of the present invention may be used as a photo-curing adhesive or for providing a minutely patterned insulating layer in a high-density printed circuit board (including a build-up multilayer circuit board) or in high-density electronic devices.
2. Description of the Related Art
Due to recent demand for size reduction, higher performance and lower cost with respect to electronic apparatuses, there has been a rapid development toward sophistication of printed circuit boards and high-density packaging of electronic devices, which has led to an active study as to a build-up multilayer wiring structure. In a build-up multilayer wiring structure, an insulating film is interposed between different wiring conductor layers, and the insulating film is minutely patterned to have via-holes for establishing electrical conduction between the different wiring conductor layers.
For the convenience of explanation, reference is now made to FIGS. 1 and 2 of the accompanying drawings for more specifically describing the build-up multilayer wiring structure. FIG. 1 is a fragmentary sectional view showing a conventional build-up multilayer wiring structure, whereas FIG. 2 is a perspective view showing a glass mask used for making such a multilayer wiring structure.
Referring first to FIG. 1, the conventional build-up multilayer wiring structure includes a first wiring conductor pattern 2 formed on each surface of a core substrate 1 which is provided with through-holes 1a (only one shown in FIG. 1). The first wiring conductor pattern 2 on one surface of the core substrate 1 is electrically connected to the first wiring conductor pattern on the opposite surface of the core substrate by way of the through-holes 1a.
Each surface of the core substrate 1 is also formed with an insulating film 3 which is suitably patterned to have via-holes 3a. Further, the surface of the insulating film 3 is formed with a second wiring conductor pattern 4 which partially extends into the respective via-holes 3a into electrical conduction with the first wiring conductor pattern 1. Depending on a particular need, an additional insulating film (or films) similarly formed with additional via-holes and an additional wiring conductor pattern may be provided to enhance the degree of circuit integration in the thickness direction without increasing the two-dimensional size (i.e., width and length).
The build-up multilayer wiring structure described above may be made by the following process.
First, a core substrate 1 is prepared which is provided with through-holes 1a and a first wiring conductor pattern 2. Each of the through-holes 1a is filled with an insulating resin 5.
Then, a photosensitive resin is uniformly applied to each surface of the core substrate 1 for forming a photosensitive resin layer 3.
Then, as shown in FIG. 2, a glass mask 6 is held in contact with the applied photosensitive resin layer 3 (which is not cured yet), and the photosensitive resin layer is irradiated with light. The glass mask 6 has impervious spots 6a, so that the portions of the photosensitive resin layer 3 corresponding to the impervious spots 6a are not exposed to light and therefore does not harden.
Then, the resin layer 3 is developed with a developer liquid and thereafter heat-treated for removal the developer liquid. As a result, via-holes 3a are formed at the portions of the resin layer 3 (insulating film) corresponding to the impervious spots 6a of the glass mask 6 by removal of the non-cured photosensitive resin.
Then, a conductor layer is formed on the patterned insulating film 3 by electroless plating or electroplating.
Then, the conductor layer is suitably etched to form a second wiring conductor pattern 4.
The degree of circuit integration may be increased by repeating the above process steps.
As a material for forming an insulating film in a build-up multilayer wiring structure or the like, a photosensitive resin composition is known which contains bisphenol epoxy acrylate, a photosensitivity enhancer, an epoxy compound and a curing agent for example (see JP-A-50-144431 and JP-A-51-40451). However, such a resin composition requires a large quantity of an organic solvent for development, so that sufficient care needs to be taken for avoiding environmental pollution and a risk of fires.
Recently, therefore, use is made of a photosensitive resin composition which can be developed with a dilute alkaline water solution in place of an organic solvent. For instance, JP-A-56-40329 and JP-A-57-45785 disclose an alkaline-developing type photosensitive resin composition containing, as a base polymer, the reaction product of an epoxy resin and an unsaturated monocarboxylic acid, to which is added a polybasic acid anhydride. Further, JP-A-61-243869 discloses an alkaline-developing type photosensitive resin composition containing novolak epoxy, this resin composition providing a good chemical resistance.
However, the epoxy-based photosensitive resin composition of the prior art described above has a glass transition temperature (Tg) of no higher than 150.degree. C., so that it fails to provide a sufficient heat-resistance. Further, since the prior art resin composition also contains a filler such as calcium carbonate in a proportion of no less than 10 wt % relative to the epoxy resin, it may fail to provide a sufficient electrical insulation if the insulating film made of the resin composition is thin or if the intervals between the wires of the wiring conductor pattern are narrow (i.e., if the wiring conductor pattern is formed excessively fine).